1. Field of the Invention
The present general inventive concept relates to a method of controlling a transfer voltage for an image forming apparatus, and more particularly, to a method of controlling a transfer voltage using an ambient temperature sensed by a temperature sensor.
2. Description of the Related Art
In general, image-forming apparatuses may include laser beam printers, a LED printer head (LPH) printers, facsimile machines, and so on. The image-forming apparatuses perform a print operation through charge distribution, exposure, development, transfer and fusing processes.
FIG. 1 is a view illustrating a general image forming apparatus. Referring to FIG. 1, the image forming apparatus includes a photosensitive drum 10, an optical scanning unit 12, a developing unit 13, a transfer unit 20 having a transfer belt 14, a transfer roller 21, a fuser roller 22, and so on.
The photosensitive drum 10 is also called an Organic Photo-Conductive (OPC) drum. The photosensitive drum 10 is a part on which an image is formed using light before the image is printed on a printing paper P, and its surface is charged with a uniform high voltage by a charge roller (not illustrated).
The optical scanning unit 12 is also called a laser scanning unit (LSU), and forms a latent image on the surface of the photosensitive drum 10 by outputting the light corresponding to the image on the rotating photosensitive drum 10. The latent image formed on the surface of the photosensitive drum 10 by the optical scanning unit 12 is called an electrostatic latent image.
The developing unit 13 converts the electrostatic latent image on the surface of the photosensitive drum 10 into a visible image using toner particles. In a case of a color image forming apparatus, the developing unit 13 is provided with toners of colors, such as yellow, magenta, cyan and black, and mixes the toners of the respective colors in the order of yellow, magenta, cyan and then black to enable a desired color to be printed.
The converted visible toner image is transferred to the transfer belt 14 by a photosensitive transfer roller 16. The transfer belt 14 is driven and rotated along an endless track by a driving roller 19 and a plurality of rollers installed on a path of the endless track. The plurality of rollers include a backup support roller 15 that is rotated as the driving roller 19 is rotated, a nip roller 17 and a tension roller 18 for adjusting tension of the transfer belt 14. Also, the transfer roller 21 is in contact with one side of the transfer belt 14.
A high-voltage terminal 24 is connected to the transfer roller 21. By a high voltage applied from the high-voltage terminal 24, the transfer roller 21 moves the visible toner image transferred to the transfer belt 14 to a front surface of the printing paper P. At this time, since the toner image moves to the front surface of the printing paper by a weak electrostatic force of the transfer roller 21, the toners may be scattered due to an external influence. Accordingly, the fuser roller 22 melts and firmly fuses the toner image to the printing paper P by applying heat and pressure to toner particles of the toner image that have moved to the printing paper.
According to the general image forming apparatus, however, a characteristic of the toner image fused on the printing paper P is changed according to a transfer voltage applied to the transfer roller 21. Specifically, if the transfer voltage is low, the toner image is not efficiently stuck on the printing paper P due to a weak electrostatic attraction force generated from the transfer roller 21, and an image trembling phenomenon occurs. By contrast, if the transfer voltage is high, the toner particles of the transfer belt 14 is inversely charged to make the toner image not stuck on the printing paper P, or the toner image is scattered before it is transferred to the printing paper P due to an electrostatic attraction force generated from the transfer roller 21.
Accordingly, it is necessary to properly adjust the transfer voltage in accordance with a resistance value of the printing paper that passes through the transfer roller, and a resistance value of the transfer roller. Especially, since the resistance value of the printing paper and the resistance value of the transfer roller are sensitive to an ambient temperature, the transfer voltage should be properly adjusted in accordance with the ambient temperature.